JP5959855B2 - Flexo printing process with wet-on-wet function - Google Patents

Description

  The present invention is based on the deposition of a polymer or segment thereof in an ink formulation and is controlled to cause the formation of a gel with the appropriate mechanical strength that enables the required color trapping for wet-on-wet flexographic printing processes. The present invention relates to a flexographic printing process having a wet-on-wet function enabled by gel formation. This controlled deposition is always achieved by controlling the Hansen solubility parameter of the ink system. This wet-on-wet printing process, with or without intermediate air drying, greatly reduces the use of energy without significantly reducing or expelling volatile organic compounds (VOC), and only one last This is possible by a curing step with UV or EB irradiation. The present invention also relates to an ink and printing apparatus for performing this process. This process is also suitable for letterpress printing.

BACKGROUND OF THE INVENTION Flexographic printing has become a major printing process for producing flexible packaging for food and non-food products, particularly in North and South America, and in Europe it plays a role almost equivalent to gravure production. Sharing.

  In Asia and the Middle East, the share in which flexographic printing is involved is still growing as its quality has grown and the ability to print Asian characters is now readily available.

  Flexo printing has since been invented an anilox roll that provides more consistency to the inking process, and reduced exposure to volatile solvents present in the ink, and hermetically sealed to maintain ink viscosity for a longer period of time. Many improvements have been achieved, such as the introduction of an ink chamber. Photopolymers are certainly one of the biggest contributions to quality, followed by direct laser engraving over the last decade. All of these contributions force the development of better inks, and one of the most important factors of these better inks is their color intensity.

  There is a close similarity between print quality and screening resolution, anilox screening and the amount of ink, especially the color intensity of the ink. To improve print quality, it is essential that the screening we use is also increased. Gravure and offset use 150-200 lines per inch, while traditional flexographic screening requires a range between 100 and 140 lines per inch. The ability to avoid the smallest dots in the plate from entering the anilox cell limits the relationship between plate screening and anilox screening, which is about 6 for anilox than for plate. This is because it is 8 times larger.

  To print 200 lines per inch, anilox with 1200 to 1600 lines per inch is required, and as the anilox line increases, a new YAG laser engraving technology to deliver high capacity to the anilox roll Even with the use of ink, the amount of ink transferred rapidly decreases and there is still a need for stronger inks to achieve specific color densities for printing.

Table 1 below shows the standard anilox charters that are currently available for flexographic printing.

  The capacity reduced by the high anilox screening shown above, for conventional flexo inks, contains 50% to 70% solvent in their compositions, increasing the pigment loading in the ink. As a result, the possibility of increasing the color intensity of the ink is reduced, which is one of the major limitations.

  Increasing complexity to obtain the high color density required by the flexographic printing process and transferring all the ink in the anilox to the substrate is due to the ink layer remaining partially on the anilox roll and on the printing plate surface It's not easy.

  High volatile organic compounds (VOC) and low density color intensity are two major unresolved issues for flexographic printing, and the next challenge to be achieved: obtaining a better ink and likewise Consists of developing environmentally friendly inks for flexographic printing processes.

  US Pat. No. 5,690,028 relates to a viscous radiation curable ink and a reduction in its ink viscosity by heating it prior to application. After application, the ink layer cools and the viscosity again increases enough to support other color overprints, giving satisfactory color trapping. The main disadvantage verified with respect to US Pat. No. 5,690,028 is to control the temperature of the ink and ensure that no significant changes occur during the printing process.

  Other inventions have attempted to solve these problems in many different ways. In US Pat. No. 6,772,683, which is incorporated herein by reference, viscosity controlled dilution in which wet trapping of continuously applied ink layers is performed by controlling the time between the ink layers. It has been proposed to use a low viscosity flexographic ink with an agent. However, it takes too long to evaporate the solvent.

  U.S. Pat. No. 7,479,511 uses an aqueous solution that uses a concept similar to that of U.S. Pat. No. 6,772,683, above, as to how an ink layer can be overprinted. Although a formulation is disclosed, this again focuses on the mobility of the reactive material inside the final coating, since lack of molecular migration can result in low conversion after the curing process.

  In addition, US Pat. No. 7,479,511 also uses some moisture retention to ensure the required mobility of the system in order to achieve the desired conversion. The exact amount of water has been proposed as a compromise between the minimum retention level in flexographic printing and the ability to withstand the overprinting process.

  PCT / US2005 / 012603 proposes a layered material having two or more layers that can be cured by exposure to highly accelerated particles such as electron beams. The layered material includes a substrate, an ink formulation on at least a portion of the substrate. The ink formulation comprises an ink and a monomer curable by free radical or cationic polymerization and a lacquer comprising at least one monomer curable by free radical or cationic polymerization.

  The solution discussed above requires a high investment for adding ultraviolet irradiation (UV) or electron beam irradiation (EB) equipment, and even the cost of that ink is high compared to conventional solvent-based inks. Those patents are rooted in exactly the same principle as occurs in conventional solvent-based systems, because the intermediate drying in common impression cylinder flexographic presses is not strong enough to result in a completely dry ink layer.

  Evidence that interstation drying of the flexographic printing process cannot ensure complete drying of the ink is given by continuing research on low tack resins for flexo solvent inks, which are inks that are not completely dry This creates a problem for printing processes including color trapping and plate dust, among others.

  On the other hand, the increased viscosity ink discussed above results in difficulty reaching the total conversion of the fully reactive material due to the low mobility caused by its high viscosity, which is described in US Pat. No. 7,479,511. Is the problem that we are trying to solve by leaving some amount of water up to the moment the ink passes through the curing system (EB or UV) and satisfying the complex balance of water presence.

The object of the present invention is to provide a flexographic printing system and process that includes an overprint color process that contains no solvent or a reduced amount of solvent, while at the same time having a higher degree of color intensity, It is an object to provide an ink that exhibits good adhesion to the major substrates on the market.

  Another object of the present invention is the ability to print on a wet-on-wet basis and cure by ultraviolet irradiation (UV) or electron beam irradiation (EB) only at the end of the process, ie when leaving the press. Ink composition.

SUMMARY OF THE INVENTION The object of the present invention can be achieved by providing a flexographic printing process that includes gelation of ink once applied to a substrate, said method comprising two important principles: a substrate. Characterized by the gelation or gel formation of the above ink and the use of Hansen solubility parameters leading to this gelation. This process uses a reduced volatile organic compound (VOC) content, which means a reduction in the amount of solvent, and at the same time has a higher color intensity, good for the main substrates currently on the market This is an overprint color process that exhibits excellent adhesion.

In this method, the Hansen solubility parameter of the ink can be changed by a known method .

  The invention also relates to a combination of a polymer and a liquid mainly consisting of radiation curable monomers and / or oligomers, diluents, colorants, additives and / or photoinitiators, and optionally a small amount of non-reactive solvent. Disclosed is a flexographic ink that is curable by UV / EB irradiation, which is a constructed gel. These compounds are combined to produce a system that has the ability to form a gel during what is commonly referred to as the drying stage of the flexographic printing process. Controlled gels arise from the absence of a dissolving action in a liquid medium from the precipitation of polymer chain networks, or polymer segments that form such networks. This process can be understood by the Hansen solubility parameter, discussed in more detail below, and can therefore be controlled as much as possible.

1 shows a schematic illustrating the theory of changing and / or controlling the Hansen solubility parameters supporting the present invention. 1 shows a schematic illustrating the theory of changing and / or controlling the Hansen solubility parameters supporting the present invention. Figure 2 shows a diagrammatic representation of a traditional flexographic printing press. 1 shows a flexographic printing press containing an EB function. 1 shows a flexographic printing press containing a UV function. A micrograph of a gel network formed by polyvinyl alcohol in water with a characteristic structure of the polymer and a large volume of free space filled with liquid is shown, as well as a nanoscale structure of the polymer network of the hydrogel. The bar (lower right) represents 0.2 micrometers. L. Pakstis and Pochan; From Science News, Vol. 161, No. 21, May 25, 2002, p. 323. Some desirable monomers such as HDDA (1,6-hexanediol diacrylate), TMPTA (trimethylolpropane triacrylate), TRPGDA (tripropylene glycol diacrylate), and some most desirable solvents such as common 1 schematically shows a Hansen solubility parameter chart including positions such as glycol ethers and esters. Represents an evaluation chart of volatile organic compound content during printing time, the low level volatile organic of the present invention having a peak volatile organic compound of less than 25 mg C / Nm ³ (milligrams of carbon per cubic meter of air) FIG. 2 demonstrates a compound. Various configurations of flexo inking systems capable of operating gelled flexo inks are shown. Various configurations of flexo inking systems capable of operating gelled flexo inks are shown. Various configurations of flexo inking systems capable of operating gelled flexo inks are shown. Figure 2 shows a graph of gel hardness versus gelling agent concentration for polyvinyl butyral (Butvar B76).

Detailed Description of the Invention The following definitions are used in this description.

  Viscosity is defined as the resistance to changes in shape or movement of adjacent parts of a fluid (liquid or gas) relative to each other. Viscosity means a corresponding relationship to flow. The reciprocal of the viscosity is the degree of fluidity and flowability. For example, molasses has a viscosity greater than water. Since fluid parts that are forced to move carry some adjacent parts together, viscosity can be thought of as internal friction between molecules, and such friction resists the development of velocity differences in the fluid.

  For many fluids, the tangential or shear stress that causes flow is directly proportional to the resulting rate of shear strain or rate of deformation. In other words, the shear stress divided by the shear strain rate is constant for a given fluid at a fixed temperature. This constant is called dynamic viscosity, or absolute viscosity and often simply viscosity. (Encyclopedia Britannica) Z. Rogovina proposes the following definition for a gel in 2008 Polymer Science Series C ISSN 1811-2382 (printed) 1555-614X (online) DOI 10.1134 / S181122088010050: “Gel is composed of at least two components One (polymer) forms a three-dimensional network (chemical gel and physical gel, respectively) in the medium of other components (liquid) by covalent or non-covalent bonds. In that case, the minimum amount of the liquid is sufficient to ensure the elastic properties of the gel, even though it can exceed 10-100 times the amount of the polymer. In the polymer chain stiffness, It is noted There it is possible to form a gel. Common feature of physical gels is the presence of a yield point. "

  The same author also published the following gel definition in 1974: “Gel is a polymer-solvent system in which polymers present at very low concentrations form a very stable three-dimensional network in the solvent. It should be considered that the network is a property of the gel formed by both chemical and physical bonds, and it is noted that the change in temperature is mainly reversible between the gel and the solution. A second group of gels that cause metastases. "(L Z Rogovina et al., 1974 Russ. Chem. Rev. 43 503-523 DOI: 10.070 / RC 1974v043n06ABEH001821).

  The definition of Hansen solubility parameters found in Wikipedia is simple but complete and accurate.

  The Hansen solubility parameter, also termed the inverse principle of dissolution, was developed by Charles Hansen as a way to predict whether one substance will dissolve in another to form a solution. They are based on the idea that similar things dissolve similar things, and when one molecule binds in the same way as itself, it is defined as "similar" to another molecule.

Specifically, each molecule is given three Hansen parameters, each typically measured at Mpa ^0.5 .
・ Δ Energy from dispersive bonds between _d molecules ・ δ Energy from polar bonds between _p molecules ・ δ Energy from hydrogen bonds between _h molecules

These three parameters can be treated as coordinates for a point in three dimensions, also known as Hansen space. Two more similar molecules are in this three-dimensional space, on the contrary they merge into each other. In order to determine whether the parameters of the two molecules (usually solvent and polymer) are within range, a value called the interaction radius (R ₀ ) is given towards the material to be dissolved. This value determines the radius of the sphere in Hansen space, the center of which is the three Hansen parameters. To calculate the spacing (Ra) between Hansen parameters in Hansen space, the following equation is used:
(Ra) ² = 4 (δ _d2 −δ _d1 ) ² + (δ _p2 − (δ _p1 ) ² + (δ _h2 −δ _h1 ) ²
When this is combined with the interaction radius, the relative energy difference (RED) of the system:
RED = Ra / R ₀
Is given,
When RED <1, the molecules are similar and dissolve, when RED = 1, the system partially dissolves, and when RED> 1, the system does not dissolve.

  To summarize the differences between these concepts, a gel is defined as a two-phase system composed of a solid network phase swollen by a liquid phase instead of a single phase of a viscous homogeneous liquid. Is done. In fact, the establishment of two phases by a second order transition at the instant of gelation instead of a first order transition of viscosity increase is a significant difference between the two phenomena.

Also, a very important difference between a gel and a viscous liquid is the fact that the gel does not have a defined viscosity, because the gel has a yield value until the gel breaks. After that, there is no change in formulation and temperature, just at the applied shear rate, and the gel exhibits an infinite viscosity making it impossible to define the exact viscosity.

  Wet trapping, or wet-on-wet ink printing, is when the first layer of ink deposited at the first inking position is dried when the second layer of ink is superimposed on that first layer at the second inking position. The printing process has not been completed. Wet trapping is disclosed, for example, in US Patent Application Publication No. 2003/0154871.

The first object of the present invention is to
a) printing on a substrate a first layer of radiation curable ink suitable for wet-on-wet flexographic printing, said ink comprising one or more non-reactive polymers and optionally one or more non-reactive polymers; Comprising a combination of at least one reactive monomer and / or oligomer, pigment, and additive of a reactive solvent, whereby the polymer (s) comprises the monomer (s) and / or oligomer (s) Or only after partially adding a non-reactive solvent,
b) bringing the printed first ink layer into a gel state, the gel ink layer having sufficient strength to withstand subsequent printing steps;
c) Subsequently, a second ink layer in a liquid state is printed on at least a part of the first gel layer that has been previously gelled, and the second ink layer is changed into a gel layer simultaneously with the printing. Steps,
d) printing all series of ink layers following steps a) -c) until the time when all colors are applied on the substrate;
e) curing the entire ink layer simultaneously using EB or UV radiation at the end of the method.

  The desired multi-layer overprint required by this method is achieved by forming a gel in each applied layer, then applying the next layer, and finally curing the multi-layer ink film with appropriate radiation (UV / EB). Is done. This mechanism exists in all conventional flexographic printing processes and is completely different from the normal liquid viscosity increase employed in previous techniques such as described in the above-mentioned patents.

  Control of the gelation process is such that the Hansen solubility parameter of the media is adjusted and / or so that the ink system cannot keep the selected polymer, or segment of the selected polymer, truly dissolved, i.e. in solution. Or best achieved when changed. The end result of this controlled insolubility is the precipitation of the polymer, or polymer segment, causing the formation of a swollen gel with contacts where the polymer or polymer segment intersects. These polymer entities cannot "join" together and exist in a liquid with controlled insolubility. In other words, the insoluble polymer entities seek each other with similar / equivalent Hansen solubility parameters. They cannot be present in a liquid where the Hansen solubility parameter is too different to allow dissolution, as described in more detail below.

  The controlled gelation process results in a network of polymer chains that resembles a solid-like system for forces that are active in the overprint flexographic printing process. This relative strength is why the wet-on-wet overprint process is successful. Each gelling layer has the ability to support itself and accept subsequent color layers without problems.

  The precipitation or gel formation process can be controlled to occur, for example, even when only a small portion of the non-reactive solvent is present and distilled off. Some polymers are made up of separate blocks or segments that are covalently bonded into one large molecule. If some polymer segments are not dissolved by the monomers and oligomers that form at least part of the “solvent” medium of the ink, while other polymer segments are reliably dissolved by them, the insoluble segments Appropriately gelled systems physically coupled by can function without the use of non-reactive solvents or by using these limited amounts. In such cases, only a shearing force can convert such a reversible gel into a liquid that rapidly reforms on the printed surface. An example of such a system is a polyester (or oil-modified polyester) that also has polyamide blocks or segments. The solubility properties of the different polyester parts compared to the polyamide parts allow gelation based on the insolubility of the polyamide parts in each other in a liquid that indeed dissolves the polyester. In principle, the reverse gel can also be generated by dissolving the polyamide segment and precipitating the polyester segment, but the liquid required for this is necessary to dissolve the polyester both environmentally and in practice. It ’s not as convenient as it is. This type of dihedral polymer can also tolerate the significantly smaller amounts of non-reactive solvent needed to produce the desired gel.

  The gel films produced by the method of the present invention can be overprinted much faster and more easily than those formed by prior art viscosity increase mechanisms, which can be obtained by offset printing. An excellent trapping characteristic is provided which is generally much better than the trapping characteristic.

  During deposition, the polymer creates a network in the media, resulting in a solid-like system against forces acting in the overprint flexographic process, and the possibility of performing the overprint process, i.e. preprinted. Creates the ability to support and accept other color layers on top of the object. In a flexographic printing process, the gel is formed instantaneously when applied in a very thin layer with very high color strength ink. Layers applied in flexographic printing vary on average between 0.3 and 2.5 microns. Under the influence of the surface energy from the substrate and the previously applied ink layer (if any), the gel formed in the printing process can be considered instantaneous gel formation.

  Gel strength is expressed by giving the gel hardness on an appropriate scale, such as Shore 00 as measured by the ASTM D2240-05 standard test method for rubber properties, prior to gel curing. And confirm. In order to determine the desired gel hardness under laboratory conditions, preparation of a sufficiently large (several hundred grams) ink sample is required due to the size of the durometer.

  This flexographic printing involves the gelation of ink once applied to the substrate in a completely different manner and has found a solution to the compromise between wet trapping and cure. The solution to the problem resides in very different system states, ie gels, not in concentrated solutions. One skilled in the art is provided with two important principles and differences by the present invention. These are the gelation or gel formation of the ink on the substrate and the use of Hansen solubility parameters to reach this gelation.

  In addition, any agitation that occurs during the printing phase stops after the ink is deposited on the substrate, substantially assisting in gelling the applied ink layer.

  The gel state is defined as a solid by the main investigators of this object, but it is a solid with a very large degree of liquid mobility inside the system and at the moment it hardens by an exothermic reaction. It is also in a state where it can be returned to the liquid state by a certain amount of heat in the same row as that generated.

  For example, the movement caused by shear forces also has blocks or segments in which the polymer forming the gel does not dissolve in the liquid phase, while some other part of the polymer is in the liquid phase. When truly dissolved in the gel, the gel can be converted to a liquid. The shear force is sufficient to pull away the gelled segments, which can allow them to re-form the gel when there is no longer any external shear force. This state can also be used to produce inks similar in quality and performance to those containing small amounts of non-reactive volatile solvents. In either case, control of the Hansen solubility parameter in the ink is necessary as discussed below.

  The present invention refers to a flexographic printing process having a wet-on-wet function (wet trapping) based on gel formation or temporary disintegration of the flexographic ink by controlling the Hansen solubility parameter of the ink system. The mechanism for obtaining the desired wet-on-wet color trapping is based on gel formation in the applied ink using controlled physicochemical mechanism polymer deposition. This leaves behind a liquid that does not dissolve a given polymer or segment thereof by controlling the Hansen solubility parameter, for example, by heating, i.e., distilling off, a non-reactive and volatile solvent. Can be done.

  This flexo printing process with wet-on-wet function is based on cure by controlled precipitation leading to gelation of the ink formulation, with or without intermediate air drying. By applying heat, changing the Hansen solubility parameter of the ink system and curing by the last radiation means. This process can use radiation curable inks and all colors are cured only after being applied to the substrate. The flexo ink has a viscosity of less than 4000 cps, preferably less than 2500 cps, and most preferably less than 1000 cps when it is applied to the final substrate.

  The present invention examines in detail what can be defined as reverse solubilization, and determines the Hansen solubility parameter of the medium to obtain a somewhat modified degree of solubilization or solvation of the selected polymer, flexo overshoot. Control or change to produce a layer of ink, such as a gel or solid, with sufficient strength and stiffness to support the printing or letterpress printing process.

  The great advantage of this principle is that this phenomenon can be caused by very low levels of solvent due to the operational basis of the Hansen solubility parameter. The choice of polymer and liquid that make up the final formulation is such that reactive liquids that are incompatible in the gel are just solvated if the polymer is just at the solubility boundary or a given segment of the polymer. This can be done to have a Hansen solubility parameter. By changing the solubility parameter of a reactive liquid with a very small change in the amount of the appropriate solvent or with the correct Hansen solubility parameter, it can be adjusted from liquid to gel or vice versa.

  The present invention, based on the gel formation of the ink during the printing process, i.e. between two adjacent inking stations, allows a smooth implementation of the overprinting process. As seen in FIG. 6, the present invention takes advantage of both the migration of low viscosity liquids through large free spaces in the polymer gel network and the breaking of the gel during curing. This gel breakage is caused by the heat generated by the exothermic chemical reaction during curing. It is well known that physical gels are very sensitive to heat. The film once again becomes liquid or liquid and flows together to form a strong cured print. The dissolution zone shown in FIGS. 1, 2 and 7 increases at higher temperatures, and a liquid with a Hansen solubility parameter just outside the boundary of dissolution at room temperature is a good solvent at higher temperatures. In the present invention, this effect helps the desired breakage of the gel at high temperatures. This concept is the basis of the second embodiment of the ink, which is first prepared such that the gel-like ink is just outside the solubility boundary at room temperature.

  The high mobility of the reactive components during the gel curing process and after the temperature is raised during the curing stage and the gel is destroyed ensures a high degree of chemical conversion without any additional control or equipment Is done.

  This flexographic process is less than 4000 cps, preferably 2500 cps from the gel state by applying agitation ink, i.e. stirring or heat, as described above, so that it can be applied by the ink system present in the flexographic press. A flexographic press equipped with means for heating or subjecting a shearing force to a gel ink suitable for changing to less fluid ink is used.

  Therefore, it is a further object of the present invention to have a flexographic printing press with means for heating the ink before applying it to the final substrate and / or means for applying agitation or shear forces.

  The flexographic printing press according to the present invention is less than 4000 cps from the gel state by applying agitation ink, i.e. stirring or heat, as described above, preferably in order to be able to be applied by the ink system present in the flexographic printing press. Comprises means for heating or subjecting the gel ink to a shear force suitable for changing to a fluid ink of less than 2500 cps.

  As shown in the figure, the machine comprises ink transfer means including an anilox roll and a printing plate, and further, excess ink applied on the anilox roll, with or without a sealed chamber, Like a blade applied in a gravure or a conventional flexographic printing system, it is provided with a cleaning means for removing so as to leave ink only inside the anilox roll cell.

Figures 9 to 12 do not exclude different designs, but show possible designs for new flexographic presses, which cover a range of reasonable possibilities, especially the flexographic printing machine to direct use of the gelled ink, shows a simple way to easily adapt than traditional solvent-based flexographic inks, such as IroFlex ^trademarks and FlintGroup made FlexiRange ^trademark Toyo ink.

  More specifically, FIG. 9 shows a flexographic printing press having a common impression cylinder and two different supply systems under references 1 and 2. In Reference 1, an automatic or manual supply system (1.2) that supplies ink to the ink tray (1.1), and the ink tray (1.1) provides ink directly to the anilox roll (1.3), It has been shown to be cleaned by a doctor blade (1.6) and then inked into a plate on a plate cylinder (1.4) and ink applied from the plate to the substrate. A contention can (1.5) is installed under all inking systems to avoid contamination of other colors in the event of a leak.

  Furthermore, FIG. 9 has an automatic or manual supply system (2.2) for supplying ink to the ink tray (2.1) under the reference 2, and the ink tray (2.1) can supply ink. The amount of ink fed to the metering roll (2.3) and transferred again to the inking roll (2.4) is reduced and fed from the inking roll to the anilox roll (2.5), which is a doctor blade (2.8) shows a flexographic press that is cleaned by a plate, then inked into a plate on a plate cylinder (2.6), and ink is applied from the plate to a substrate (not shown). A contention can (2.7) is installed under all inking systems to avoid contamination of other colors in the event of a leak.

  FIG. 10 shows two other possible configurations of an inking system for manipulating gel ink. Below the reference 3, there is shown a supply system (3.2) for feeding the ink tray (3.1), which is applied to the anilox roll (3.4). After the amount of ink to be controlled is controlled by the metering roll (3.3), the ink is fed directly to the anilox roll, then excess ink is cleaned by the doctor blade (3.7) and then left on the anilox roll The ink is applied to the plate cylinder (3.5), and the ink is applied to the substrate from the plate. A contention can (3.6) is placed under the entire inking system to contain leaked ink if there is a leak and avoid contamination of other colors.

  Reference 4 on FIG. 10 shows a different inking system without a conventional ink tray, replaced by a system similar to that used in the field of solventless laminators, where a supply system (4 The gel-like ink reservoir (4.3) supplied automatically or manually according to .2) is formed by the low-speed metering roll (4.1) and the medium-speed metering roll (4.4). The medium speed metering roll applies a sufficient amount of ink to the anilox roll (4.6) to completely cover it, the blade (4.5) removes this excess ink and the plate cylinder (4.7) ) As a very thin layer on the printing plate attached to it, and then finally transferred to a substrate. As in the other examples, a contention can (4.8) must be applied to prevent color contamination in the event of ink leakage.

  As shown in FIGS. 3, 4, 5, 9, 10 and 11, the machine includes ink transfer means including an anilox roll and a printing plate, and further removes excess ink applied on the anilox roll. With or without a sealed chamber, it is equipped with a cleaning means that removes ink so that it remains only inside the anilox roll cell, such as a blade applied in gravure or conventional flexographic printing systems.

  After printing, the temperature drops again to the desired range, agitation is stopped and the ink is again brought into the gel state. The printed ink layer is gelled on the substrate surface and all those layers show sufficient stiffness to ensure wet trapping of the next incoming color until all colors are applied, then Exposure to radiation energy that initiates curing / polymerization of the curable component of the ink. This embodiment has the advantage of providing a flexographic ink that is free of organic solvents, ie, free of volatile organic compounds. Such properties are of paramount importance to the printing process and the equipment economy.

  Current flexographic printing techniques use 6-12 sequential colors to achieve the final result, but applying more than 4 or 5 colors on top of each other is a trapping problem, which is a traditional solvent based Even with this ink, it is extremely rare because the thicker the ink layer, the more serious it becomes.

  FIG. 3 shows a traditional flexographic printing machine, a common impression cylinder (CD), an anilox cylinder (1), a plate cylinder (2), a dryer (3), and a doctor blade encapsulated (4). It is shown.

  As previously stated, the present invention relates to an EB or UV curing unit at the end of the process as shown in FIG. 4 for the EB function when the substrate leaves the last tunnel dryer (5) if it is not already present. The UV function can be implemented without modification of the mechanical device other than by adding as shown in FIG.

  According to FIG. 4, the substrate is taken from the unwinder (U) to the common impression cylinder (CD), then to the last tunnel dryer (5), then to the electron beam device (EB) and then to the winder. Moved to machine (R). A similar path is found in the situation shown in FIG. Here, after passing through the last tunnel dryer (5), the base material reaches the chill roll (6) and the ultraviolet device (UV) as the lamp and the reflector, and then reaches the winder (R).

  The main problem with using these inks, especially in the flexographic printing process, is the management of inks that are in a gel state, which requires time to heat the ink and the pump systems of conventional flexographic presses are within that system. This is because it is greatly affected by the presence of high viscosity ink.

  The extension of the tube that directs ink through the inking system is also a source of more problems and difficulties for the printing press. To solve these problems and because the ink can exhibit a formulation free of volatile organic compounds, the solution can be associated with the use of a different flexo inking system without a doctor blade system.

  The present invention also includes a polymer and a liquid combination consisting primarily of radiation curable monomers and / or oligomers, additives, photoinitiators, and optionally a small amount of a non-reactive solvent, wherein the polymer is a gelling agent. A gel-like flexographic ink that is curable by UV / EB radiation acting as

  All components used in this ink have a Hansen solubility parameter, and this flexographic ink is a gel with the necessary physical properties if normal, usually by mechanical or thermal action. It is brought into a liquid state during the printing process and becomes a liquid suitable for use in flexographic printing (eg less than 4000 cps, most preferably less than 2500 cps), which returns to the gel state after being applied to the last support.

  For such ink formulations containing a solvent to adjust the solubility parameter, the time to evaporate sufficient solvent to form a gel state allows the correct gel hardness relative to the measured value. However, since the gel is also formed by partial removal of the solvent, the best measurement is preferably after removal of the solvent, e.g. after obtaining a constant weight of the sample to ensure complete solvent removal. Is taken 15 minutes after the temperature of the prepared formulation has reached that room temperature.

  For solventless ink formulations, 30 minutes is typically required to build a gel of several hundred grams of sample for a constant and stable measurement.

  First, the present invention is a gel within the range of Hansen solubility parameters that includes a non-reactive solvent that at least partially distills off to provide the required gel, and inherently has the required physical properties, During the printing process, an ink is provided that is typically brought into a liquid state by mechanical or thermal action if no non-reactive solvent is used.

If the ink still uses a solvent in the formulation, the present invention provides at least two major improvements over conventional solvent-based flexographic inks:
-Very strong inks capable of printing on a wet-on-wet basis and exhibiting a high load of pigment capacity and below 2500 cps are easily achieved thanks to the properties of the selected monomers and oligomers Done;
The resulting ink has reduced volatility, even less than 15% of the total formulation compared to prior art formulated inks with a high content of solvent using about 50% volatile organic compounds in the composition Organic compounds can be indicated.

  The combination of these two characteristics-very strong color inks and low volatile organic compounds-makes it possible to control European and US volatile organic compounds and pollution without ink or residue pre-treatment or final treatment. Gives the possibility to fit. These measures reduce the cost of the final product, improve the ink quality and contribute to environmental protection.

When a solvent is added into the ink composition, the main criteria for selecting the solvent can be summarized as follows:
a) The solvent chosen must be stable in the medium (eg avoid alcohols and glycols that can undergo transesterification to generate toxic acrylates in a short period of time).
b) Non-reactive solvents useful in the present invention should be selected from those most friendly to humans that have low skin and respiratory irritation and are compatible with the final destination of the ink (eg, food packaging).
c) To minimize the amount of non-reactive solvent added, it is a preferred choice to have a Hansen solubility parameter that is as far as possible from the Hansen solubility parameter of the last formulated mixture. The Hansen solubility parameter of the mixture is calculated by averaging the weight (or volume) of the Hansen solubility parameters of the individual components. The effect of a given component on this average is greater at the same concentration when its Hansen solubility parameter is far from the final average. This offers the possibility of greatly reducing the level of non-reactive solvent.
d) The Hansen solubility parameter and concentration of any non-reactive solvent that can be present is just within the region defined by the radius of solubility of the polymer, such as those shown in FIGS. Must reach the final position on the Hansen Solubility Chart. The distilling then causes the formation of the desired gel because it moves the Hansen solubility parameter of the remaining liquid just outside the boundary that is then determining the solubility of the polymer. This results in gel formation as disclosed above.
e) In the Hansen solubility parameter diagram, such as that shown in FIGS. 1, 2, and 7, a line connecting the averaged Hansen solubility parameters of the liquid in the formulated ink and any selected in the formulation The Hansen solubility parameter of the solvent should preferably pass through the center of solubility of the polymer, which is a low viscosity flexographic ink with a formulation of less than 4000 cps, preferably less than 2500 cps, most preferably less than 1000 cps. This is because it is the most sensitive point for effective gel breakage.
f) The boiling point of any selected non-reactive solvent that may be in the formulation is preferably greater than the boiling point of any monomer present to ensure its distillation without any noticeable loss of monomer. Low.

  With regard to the selection of the solvent for carrying out the present invention, the preferred solvent is a medium to low relative distillation rate, preferably based on a relative distillation rate criterion with the n-butyl acrylate distillation rate set to 100, preferably Between 5 and 100. The solvent should have appropriate Hansen solubility parameters for many UV / EB monomers and oligomers in order to control very low toxicity and the gel process described above.

  Preferred solvents include propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, n-propyl propio according to criteria set to select the correct non-reactive solvent for carrying out the present invention. But not limited to, nate, n-butylpropionate, n-pentylpropionate, propylene glycol diacetate, diethyl carbonate, and dimethyl carbonate. The use of non-reactive solvents with medium to low relative distillation rates such as propylene glycol monomethyl ether or dipropylene glycol monomethyl ether also improves the stability of the ink in the machine and interferes with the operator to adjust the viscosity Allows up to 72 hours of printing without. This means that the printing standards also remain constant during this time, in other words a highly desirable and stable flexographic printing process.

  Preferred non-reactive solvents used in the present system may or may not dissolve the polymer directly. This is because the monomers, oligomers, and non-reactive solvents used can have Hansen solubility parameters that are outside the solubility region / amount of polymer shown in FIGS. This is possible because it is a mixture thereof that must have an appropriate Hansen solubility parameter that allows control of the printing process as disclosed herein.

  However, the medium can be non-solvent to control gel formation for a polymer, or a given segment of polymer, after partial or complete evaporation of any non-reactive solvent in the formulation. It is essential.

  If no solvent is present in the ink, i.e., the flexographic ink is an ink that does not contain a volatile organic compound, the radiation curable phase change ink is in a reactive medium at a room temperature of 15C to about 35C. It comprises a non-curable gelling agent consisting of or containing a partially insoluble block polymer.

  The volatile organic compound-free inks of the present invention consist of the following ingredients: a cure consisting of or containing a block polymer that is partially insoluble in a medium reactive at room temperature of about 15 ° C. to about 35 ° C. Curable gelling agents should be included, including additional curable monomers and oligomers and curable or non-reactive polymers and gel accelerators, additives selected to prevent the formation of single-phase inks at room temperature at standard conditions. The ink may optionally contain a small amount of solvent.

  In summary, the method provides a preparation of a solid gelled radiation curable ink film using a formulation having a partially soluble polymer, wherein the partially soluble polymer is radiation cured. Having a block or segment that does not dissolve in the medium liquid of the ink formed by the functional oligomer and monomer. These insoluble segments or blocks are linked together in the gel so that the gel state is broken by stirring, heating or a combination of both, thereby allowing printing of a liquid ink film. To do. The printed liquid ink returns to a gelled state after printing and removal of agitation, and can thus be in a state similar to the last film in a) above. Such membranes can withstand the physical effects found during printing and also provide the color trapping required for wet-on-wet multilayer printing processes, especially flexographic and letterpress printing.

  A known organogelator suitable for converting a radiation curable printing ink free of volatile organic compounds into a gel at room temperature, which is suitable for being easily broken by temperature, stirring, or a combination of both, Overcoming the limitations that still force the formulation to contain non-reactive diluents for wet-on-wet printing processes in flexography, while at the same time requiring more pressure in letterpress printing and more difficult printing Creates a system for avoiding the use of high viscosity inks exhibiting the ability to produce suitable ink formulations.

  Preferably, the gelling agent forms a solid-like gel state in the ink medium at a temperature below that at which the ink is printed and handled by the inking system, the solid-like gel comprising two Rooted in the formation of physical gels that exhibit phases, one is non-covalent interactions such as hydrogen bonding, van der Waals interactions, non-bonding interactions, ions or coordination It is constituted by a network formed by a polymer that is not completely dissolved by positional bonds, London dispersion forces, etc., and the second phase is constituted by a medium liquid in the cavity of the polymer network.

  Through the use of physical forces such as temperature or mechanical agitation, the gels of the present invention may be close to the sol system and reversed to a liquid with only one phase to exhibit the desired viscosity for the selected printing process. it can.

  Flexographic inks based on phase change as in the present invention include photoinitiators by both free radical or cationic curing when the intended curing process is desired to be UV means.

  Photoinitiators useful for the present invention include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2-methyl-1- (4- Methylthio) phenyl-2- (4-morpholinyl) -1-propanone, 2-benzyl 2-dimethylamino 1- (4-morpholinophenyl) butanone-1, 2-dimethylamino-2- (4-methylbenzyl) -1 -(4-morpholin-4-ylphenyl) -butanone, diphenyl- (2,4,6-trimethylbenzoyl) phosphine oxide, 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester, oligo (2-hydroxy-2 -Methyl-1- (4- (1-methylvinyl) phenyl) propanone, 2-hydroxy -2-methyl-1-phenyl-1-propanone, benzyl - dimethyl ketal, and mixtures thereof, without limitation.

  The use of amine synergists such as ethyl-4-dimethylaminobenzoate and 2-ethylhexyl-4-dimethylaminobenzoate is highly recommended because of its impact on the overall cure rate.

  The range of photoinitiator is about 0.5 to about 25%, preferably about 1 to about 10% of the weight of the ink. The above view about the photoinitiator also applies to the first aspect, ie the ink with reduced solvent mentioned above.

  Desirable viscosities are less than about 4000 cps, preferably less than 2500 cps, most preferably less than about 1000 cps at application conditions (temperature and agitation), and the hardness is Shore 00 under the ASTM D2240-05 standard test method for rubber properties. And at least 4.

  The temperature difference ensuring the gel-to-liquid transition between both states is below 80 ° C., preferably below 40 ° C., ie when the desired final temperature is room temperature of 28 ° C., the application temperature is 108 Must be below 0 ° C, preferably below 68 ° C.

  An easy way to ensure a temperature drop is the cooling of a common impression cylinder for flexographic printing and a counter pressure cylinder in letterpress printing. Since the substrate surrounds those cylinders, the temperature of the applied ink is rapidly reduced, resulting in gelation.

  Inks that do not contain volatile organic compounds do not contain solvents, only monomers, oligomers, polymers (acting as gelling agents) and additives, including polyester acrylates, epoxy acrylates, acrylic acrylates, and polyurethane acrylates, One of trimethylolpropane triacrylate (TMPTA), tripropylene glycol diacrylate (TRPGDA), 1,6-hexanediol diacrylate (HDDA), n-vinylpyrrolidone (NVP), n-methylpyrrolidone (NMP), etc. Alternatively, a radiation curable medium including a plurality is formed.

  Care should be taken in selecting an appropriate polymer for practicing the present invention. The choice is actually limited by the need to find polymers with solubility limits that can be used to advantage. The final liquid ink formulation must have a Hansen solubility parameter near this limit, with control over how the Hansen solubility parameter should be changed during the printing process. Among the most compatible polymers are some polymers or copolymers of polyvinyl butyral and methyl methacrylate or other acrylic copolymers.

  When no solvent is present in the ink, i.e., the flexo ink is an ink that does not contain volatile organic compounds, the radiation curable phase change ink is partially in the reaction medium at a room temperature of about 15C to about 35C. A curable gelling agent comprising or comprising a water-insoluble block polymer.

  By the use of a composite gelling agent, such as a partially soluble polymer, the ink can have a hardness of at least 4 at Shore 00 according to the ASTM D2240-05 standard test method for rubber properties at temperatures from about 15 ° C to about 35 ° C. It is possible to form a gel state having In order to obtain the necessary fluidity for use in the flexographic printing process, the ink is heated or agitated (ie, shear is applied to the ink), or both so that the gel state is destroyed and the ink is destroyed. Has sufficient fluidity (ie, a viscosity of less than 4000 cps, preferably less than 2500 cps, most preferably less than 1000 cps) to be processed by the printing system in the manner applied to the last substrate.

  The gel-forming process in the case of the present invention is preferably a low-viscosity, as described above, in which more than 50% of the final formulation is reactive, non-volatile, always having an appropriate Hansen solubility parameter. Or, in a liquid medium composed of monomers and oligomers, very low levels of polymer in the range of between 0.1% and 10% are used and are strictly limited to physical bonding.

One very important property of gels associated with the two main concepts of the invention (gel formation and Hansen solubility parameters) is the formation of a network that gives more or less stiff gel structure (hardness) and tackiness ( tack ). It is the influence of the dissolving action of the medium on the gel strength obtained depending on the degree of. In a very weak polymer-soluble medium, the polymer molecules spread as a network rather than agglomerate in the medium, as briefly described above.

  This forms a very strong gel structure produced by the polymer network with the liquid phase inside.

  The choice of polymer and formulation of the ink composition is made to avoid phase separation (liquid-solid) when the gel system is formed. A careful balance of Hansen solubility parameters is required.

  The polymer network formed in the gel must retain a relatively large amount of liquid within the network, which is between the polymer chain and the liquid, where some level of suction, sometimes called solvation, is stretched. Means that it must be maintained. Therefore, the formation of the appropriate type of gel is related to another important concept of the invention, controlling the Hansen solubility parameter to provide the correct degree of gel strength when appropriate.

  An ink gel that is suitable for the present invention, can withstand subsequent printing, and provides wet trapping is a standard test method for rubber properties of ASTM D2240-05, at least 4 at Shore 00 due to durometer hardness. It has hardness. See: www. astm. org and ASTM Vol. 09.01 Rubber, natural and synthetic-general test methods; carbon black. Preferred hardness is at least 7 for Shore 00, most preferably at least 10 for Shore 00. The upper limit is selected according to the end use and is preferably (but not necessarily) 50 at Shore 00, more preferably 25 at Shore 00. The hardness of the gel of the prepared sample is measured at room temperature (that is, 15 to 35 ° C.) 15 minutes after the gelled ink reaches a certain weight, that is, after the solvent is completely distilled off. For solventless ink formulations, the gel hardness of the prepared sample is measured at room temperature (ie, 15-35 ° C.) 30 minutes after gel formation.

  Preferred polymers include Butvar® B76, Butvar® B79, Butvar® B90, Butvar® B98, manufactured by Solutia, Inc, Elvacite (Lucite International, Inc.). (Registered trademark) 2013, Elvacite (registered trademark) 2016, Elvacite (registered trademark) 2046, but are not limited thereto. Another suitable polymer is a dendritic polymer with different polymer segments, an example of this type of polymer being Boltorn® U3000 manufactured by Perstorp.

  The amount of polymer in the final ink composition before it is gelled is in the range of 0.5% to 15% (w / w) of the total ink composition, preferably relative to the total weight of the ink formulation. Between 1% and 5%.

  For many additional polymer and monomer and oligomer Hansen solubility parameters, ranges can be determined for formulating additional ink compositions according to the present invention.

  The precipitation of the polymer acts in a similar manner to the magnetic action applied to the iron ball medium in the radiation curable medium, diffusing its surface energy throughout the system and causing the system to gel. The precipitation or gelation can be adjusted to occur even when only a small portion of the solvent is distilled off, and can show a much faster and stronger result than an increase in viscosity.

  The radiation curable phase change ink composition also includes a curable epoxy-polyamide composite gelling agent from about 1 to about 50% by weight of the ink, more preferably from about 5 to about 25% by weight of the ink, most preferably. About 7 to about 15% by weight of the ink, but that value includes amounts that can also be outside this range.

  According to the invention, the gelation is also advantageously, but not necessarily, obtained from a non-reactive polymer containing a very small amount of solvent, depending on the polymer chosen. Useful proportions of these solvents can vary from 1% up to 15% (w / w) of the total ink composition.

  For example, if the organogelator is cationically curable (eg, the curable functional group comprises epoxy, vinyl ether, allyl, styrene and other vinylbenzene derivatives, or oxetane groups), additional cationically curable monomers or Oligomers can be included in the ink vehicle.

  Examples of cationically curable monomers include alicyclic epoxides, and preferably one or more polyfunctional alicyclic epoxides. The epoxy group can be an internal or terminal epoxy group such as those described in WO 02/06371, which is incorporated herein by reference. Polyfunctional vinyl ethers can also be used.

  Additional curable monomers and oligomers and curable and non-reactive polymers and gel-forming additives are selected to prevent the formation of single phase inks at room temperature at standard conditions.

The criteria for selecting the monomer can be summarized as follows according to the reference point referring to the position of the Hansen solubility parameter in FIGS.
a) The average Hansen solubility parameter for the final monomer / oligomer combination (one or more monomers) should not dissolve the selected polymer directly, i.e. the points in the figure for this mixture are It is outside the range of complete dissolution.
b) The average Hansen solubility parameter for the final monomer / oligomer combination is close to the polymer solubility boundary to minimize the amount of solvent used and to further exploit gel breakage due to elevated temperatures It is preferable. That is, the point representing this mixture should be very close to the solubility boundary in FIGS. 1, 2 and 7 but just outside this region.
c) The final monomer / oligomer combination must be selected to yield a low viscosity ink (less than 4000 cps, preferably less than 2500 cps, most preferably below 1000 cps).
d) The choice of monomer is tailored to the end use, for example, only some radiation curable monomers are acceptable for use to produce flexible food packaging, which is a formulation for flexible food packaging. Things mean that you must comply with national or regional regulations.
e) The boiling point of the monomer is preferably not higher than that of any non-reactive solvent that may be present to keep the monomer in the ink layer after the non-reactive solvent has distilled off. Don't be.

  The selected monomer or oligomer on the Hansen solubility parameter chart is of the type shown in FIGS. The experimental determination is indeed the most reliable, leading to the most likely value of the monomer in the solubility space, and the modification of these Hansen solubility parameter values can be expected to be minor.

  The use of experimental methods has enabled the measurement of Hansen solubility parameters for a number of UV / EB monomers that can be used advantageously with the formulations according to the invention. These values can be advantageously used, for example, based on the more sophisticated computerized plots given in FIGS. 1, 2 and 7 or if further available.

  Preferred radiation curable materials are selected without limitation from the following group: trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TRPGDA), ethoxylation. (3) Trimethylolpropane triacrylate (TMP3EOTA), ethoxylated (6) trimethylolpropane triacrylate (TMP6EOTA), ethoxylated (9) trimethylolpropane triacrylate (TMP9EOTA), propoxylated (6) trimethylolpropane triacrylate (TMP6POTA), propoxylated (3) glyceryl triacrylate (G3POTA), ditrimethylolpropane triacrylate (DTMPTA), dipropylene glyco Diacrylate DPGDA, ethoxylated (5) pentaerythritol tetraacrylate (PPTTA), propoxylated (2) neopentyl glycol diacrylate (NPG2PODA), ethoxylated (2) 1,6-hexanediol diacrylate (HD2EODA).

  The amount of monomer in the final ink composition before it is gelled is in the range of 0% to 80% (w / w) of the total ink composition, preferably 30 relative to the total weight of the ink formulation. % To 50%.

  The addition of monomers allows the combination of monomers, oligomers, and non-reactive solvents to always allow control over the Hansen solubility parameter of the formulation, giving the selected polymer a good dissolving action and low viscosity and high solids content. Useful because it brings. Monomers do not evaporate with the solvent due to their higher boiling point, and they are present in the cured ink as they react into the crosslinked ink during the final cure They are not included in the solid.

  When an oligomer is used instead of a monomer, the non-reactive polymer is incompatible with the selected oligomer and has a very low viscosity, preferably between 1000 cps and 2500 cps. Ink formulations with a should be possible. A preferred proportion of oligomer is in the range of 45% to 60% with respect to the weight of the total formulation.

  Recommended oligomers that may or may not be mixed with monomers include, but are not limited to, low viscosity epoxy acrylates, amine acrylates, polyester acrylates, and epoxidized soybean oil acrylates. The oligomer is present in an amount of 0 to 80% (w / w) of the total ink composition, and the total amount of oligomer and monomer is preferably 10% to 35% (w / w) of the total ink composition. Within range.

In this patent, the ink additive can be a diluent, a coloring agent及 beauty / or synergist.

  The reactive diluent material is preferably added to the ink, for example, in an amount of from 0 to about 80%, preferably from about 1 to about 80%, more preferably from about 35 to about 70% by weight of the ink.

  Useful colorants for the system include all major organic pigments, as in the following non-limiting list: Yellow 3, Yellow 12, Yellow 13, Yellow 17, Yellow 74, Yellow 83, Yellow 114, Yellow 121, Yellow 139, Yellow 176, Orange 5, Orange 13, Orange 34, Red 2, Red 53.1, Red 48.2, Red 112, Red 170, Red 268, Red 57.1, Red 148, Red 184, Red 122, Blue 15.0, Blue 15.3, Blue 15.4, Violet 19, Violet 23, Green 7, Green 36 and Black 7. The use of inorganic pigments such as titanium dioxide is essential for white inks and some iron pigments are desirable for certain applications.

  Additives play an important role in formulation, especially to obtain low pigment and high pigment loading and improve some final properties such as wettability, scratch resistance, foam suppression etc. of plastic substrates .

The recommended main additives, Byk 019TH ^trademark, Byk 023 ^trademarks, Byk 361 ^trademarks, Byk 3510 ^trademark, Disperbyk 163 ^trademark, Dysperbyk 168 ^TM (manufactured by Byk Chemie), Foamex N ^trademark, Airex 900 ^trademark, TegoRad 2100 ^TM , TegoRad 2500 ^trademark, Tego Dispers 651 ^trademark, Tego Dispers 685 ^trademark, Tego Dispers 710 ^TM (manufactured by Tego Chemie), Solsperse 5000 ^trademark, Solsperse 22000 ^trademarks, Solsperse 32000 ^trademarks, Solsperse 39000 ^TM (manufactured by Noveon), DC 57 ^trademark, DC190 ^Trademark , DC 200/500 ^trademark (manufactured by Dow Corning), Genorad 21 ^trademark (manufactured by Rahn) and Omnistab 510 ^trademark (manufactured by IGM Resins) can be mentioned, but not limited to these.

  The amounts of colorants and additives are within the normal range in the art. However, the type and amount of colorant affects the hardness of the gel.

Based on the concepts described in the present invention, many formulation changes of the type described herein can be implemented by those skilled in the art. There are a number of choices regarding non-reactive solvents, solvent soluble resins, monomers and oligomers that permit compliance with the claims of the present invention. Also, Hansen solubility parameters for many other monomers and oligomers are currently unknown. Such data will assist in developing ink formulations within the scope of the present invention without requiring much testing.

  The present invention also allows formulation of inks with very strong colors, which in other words allows satisfactory application of thin ink films. Such inks require a polymer together with monomers and / or oligomers to incorporate the pigment in a well-dispersed and stabilized manner in order to give a clear, glossy and pure color ink. The amount of ink applied is such that a thin ink layer is obtained, the thinner the ink layer, the more this layer is in the solid state as well as other ink layers printed thereon. It is harder because it is closer to a harder base.

Inks formulated according to the present invention can be applied on traditional flexographic presses and with conventional anilox cylinders and doctor blades, but the anilox cylinder is 480 lines / cm for the four process colors. Near and below 2.5 cm ³ / m ² (1200 lines per inch and 1.6 BCM), 250 lines / cm to 5.5 cm ³ / m ² (600 lines per inch) for white and black colors and 3.5BCM), it is desirable to improve using a blade such as Superhoned ^(TM) Gold by wide blades or Allison Systems Corp width.

  According to aspects of the present invention, to achieve wet trapping in all commissioning conditions, especially when the maximum color trapping is below 300% (up to 3 × 100% color is overprinted), A small amount of air injection is used to ensure complete removal of all of the solvent. This reduces the possibility of a residual odor or solvent being retained, especially for food packaging purposes.

Cold air is usually suitable for this purpose. This is because it is possible to avoid the gas combustion dryer energy usage significantly reduced, contributing to a reduction in CO ₂ emissions. This is possible by using the gel technique of the present invention and the destruction of the gel by the heat of reaction generated in its own curing process, thereby eliminating the need for external heating.

  Moreover, if the ink layer is thin, any residual non-reactive solvent evaporating occurs much more easily, which means the need for lower heating and faster drying. Thereby, in particular, the physical gel is destroyed by the heat generated by the polymerization reaction during the curing step of the process of the invention, and this heat of reaction is sufficient to distill off any non-reactive solvent present. As such, it can result in avoiding the use of any external heat source.

  As previously mentioned, volatile organic compound (VOC) emissions in the process of the present invention are dramatically lower and the present invention is a very low level of non-reactive solvent that requires less attention from the printer. And lower than known printing processes to yield very high solids inks that exhibit very good performance compared to any other UV / EB or solvent based / water based ink.

Table 2 below shows the comparison results for the same operating conditions.

  Table 2 above shows a comparison of solvent emissions based on UV / EB formulations designed according to the principles of this patent for conventional solvent-based inks. The end result for volatile organic compound emissions is 15 times less for the UV / EB invention ink than for pure solvent inks.

  FIG. 1 schematically illustrates the concept of the present invention based on Hansen solubility parameters. FIG. 1 uses δP, polar Hansen solubility parameter versus δh, hydrogen bond Hansen solubility parameter. All good solvents for the polymer define a soluble region (the soluble sphere because of the three Hansen solubility parameters). This is illustrated by a circle A having a center C and a radius R. All liquids, such as solvent (S) in the circle, whether reactive or not, dissolve the polymer, while monomer (M) is located outside the soluble sphere. Does not dissolve.

  FIG. 2 shows the change in Hansen solubility parameter of the ink after evaporation of the non-reactive solvent S using the same type of plot as in FIG. As observed by comparing these figures, the average Hansen solubility parameter of the liquid (F) in the ink is the boundary after removal of any non-reactive solvent from just within the boundary of the circle in the supplied state. Move just outside. The desired gel formation is then brought about.

  As previously mentioned, in a given case, it may be possible to use a polymer with special segments that do not dissolve in the supplied ink liquid with gel formation from the outset. The gel is easily degraded by shear forces in the printing process and provides a liquid that can be transferred in a printing device as described above. The gel then recovers during a step where a different color is applied in a wet-on-wet printing process. There is no significant shear force after the ink is applied, so the gel is rapidly formed again.

  Many skilled authors in the art, such as Van Kevelen and Hofsizeer (Van Krevelen, D.W .; Hoftyzer, P. J. "Characteristics of Polymers. Correlation with Chemical Structures. Correlation with Chemical Chemistry. Elsevier: NY, 1972), Hansen (Hansen, Charles (2000) “Hansen Solubility Parameters: A user's handbook” (Boca Raton, Fla: CRCH). L. Hoy, “Hoy Table of Solubility Parameters (Hoy Tables f solubilty parameters) ", Union Carbide Corp., 1985), as described by the combination of two compounds in a suitable amount, can result in a new single solvent theoretical. In the current situation, the formulated solvent F (50% monomer M and 50% solvent S) yields exactly the center point of the line connecting both S and M. Since the “new solvent” is in the solubility region, it will be able to dissolve the solvent resin A. On the other hand, monomer M has a high molecular weight and a high boiling point, and after printing in the flexographic printing process, solvent S, which is much more volatile than monomer M, begins to distill. As a result, the point indicating the solvent F blended in the figure moves toward “residual solvent”. FIG. 2 shows a new position of the blended solvent F after 50% of the solvent S has been distilled off and the monomer M has not been distilled off.

  The process continues to the point where there is no remaining solvent S, and formulation solvent F is the formulation in which monomer M is present, so what is present matches it. However, long before the situation, the compounding solvent F is outside the solubility region of the solvent-based resin A, and the solvent-based resin A is then precipitated in the medium of the monomer M to support the overprint process. Gives the ink a gel consistency that is sufficient for Experiments show inks with color trapping properties of “good” to “excellent”.

The formation of a suitable gel network in the ink after application of the ink and prior to the subsequent application of different colors, as well as radiation curing of the layered print of the entire composite, includes the following steps:
a) formulating a radiation curable ink system suitable for wet-on-wet flexographic printing by combining a non-reactive polymer and, if necessary, a small amount of non-reactive solvent with reactive monomers and oligomers;
b) A new mechanism known as Hansen solubility parameter control by evaporation of any non-reactive solvent causes non-reactive polymer precipitation and forms a gel with sufficient strength to support the subsequent color overprinting process Alternatively, a polymer having both soluble and insoluble segments in a mixture of reactive monomers and oligomers that do not contain any non-reactive solvent can achieve adequate gel strength by precipitation of the insoluble segments. By adjusting the Hansen solubility parameter only with reactive monomers and oligomers, the wet-on-wet printing function is enabled, and the shear force during ink application reversibly makes it a liquid, thus its rapid application And make sure that curing is possible. And-flops,
c) preparing all subsequent colors according to the new mechanism described above and applying the colors to complete the flexographic printing process;
d) collectively curing all ink layers simultaneously using EB or UV radiation at the end of the process;
including.

  This new mechanism is extremely beneficial and can significantly reduce or even eliminate volatile, non-reactive solvents in the formulation.

  The similarity in operational considerations between this companion ink and conventional solvent-based inks also confirms the easy adaptation of the printer to this new technology.

  In order to simplify the calculation and presentation, the Hansen dispersion parameter for the reactive monomer is not taken into account in these cases, because all other components in the system are linear in structure. This is because they do not have halogens or other large atoms of the kind that increase the dispersion parameter and are reasonably similar to these Hansen dispersion parameters.

  The following are examples of some formulations useful for illustration made according to the present invention. These examples, however, cannot be construed as limiting. Any alternatives or modifications that fall within the scope of the claims should be clearly considered to be within the scope of the present invention.

Table 3 below summarizes the Hansen solubility parameters of several commercially available conventional ingredients, including those selected for the following formulation examples.

Example 1: Ink with a small amount of solvent Formulation A is in accordance with the present invention for non-food applications containing only 5% solvent and 0.5% polymer (polyvinyl butyral-Butvar® B76) For formulated EB curable inks: Formulation A is shown in Table 4 below.

Manufactured in Comexi FW 1508 at a production rate of 350 m / min using only cold air in an interstation dryer and in the EZCure-I DF ^{trademark from} ESI (Energy Sciences Inc.-Wilmington, Mass.) And cured at 20 kGy.

The printed material was tested for adhesion by the Scotch test method. The results are shown in Table 5 below.

The formulations according to the invention exhibit the following trapping values, provided that the achieved values obtained according to the invention are compared with the minimum values obtained by known offset methods.

  It is clear that the gel strength achieved in the above formulation was not sufficient to ensure the minimum desired trapping value for all colors, even though some colors achieved slightly more than the minimum. Yes, it indicates inconsistencies and potential problems that can occur during continuous operation of printing.

In order to evaluate the above formulation, all changes to the Hansen solubility parameter before and after the 5% solvent loss for the formulation were calculated in the following Table 6 and the following formulation A was developed.

  After removing all other components of the formulation and limiting the formulation to compounds that form a solubilizing medium, Formulation A shows 83.6% TMPTA and HDDA equals 8.25% , 5% of the solvent in the total formulation gives a formulation of the liquid compound of A1 that is 8.2% of the liquid medium.

Changes in Hansen solubility parameters of the first formulation A1 (before solvent evaporation) and formulation A2 (after solvent evaporation) are shown below.

  Due to the poor trapping in the previous example, the behavior of the gel was well studied and the hardness was revealed as one of the best properties of the gel itself.

  In order to provide a measure of the hardness of the gel, a formulation comprising 5%, 4%, 3%, 2%, 1% by weight of polyvinyl butyral (Butvar B76) of the total nonvolatile content of each ASTM D2240-05 "Standard Test Method for Rubber Properties", prepared for basic colors (yellow, magenta, cyan and black) and published by Wotest Company-Rua Francesco Mosto, 55-Sao Paulo-05220-005-SP-Brazil According to (Standard Test Method for Rubber Property) ", it was measured with a Shore 00 durometer. This test method is based on penetration when a certain type of indenter is pushed into the material under certain conditions, which is an empirical test.

  A 150 g total formulation for each color and concentration was prepared and applied with a Shore 00 durometer readhead and gelled in a can to leave an unobstructed flat surface to obtain accurate measurements.

This type of durometer is usually used to measure very soft polymer foams, such as polyurethane foam used for pillows and mattresses, and the correct measurement is a series of at least three consecutive values. This is considered to be a measured value obtained when the value is stabilized by measurement. This test was performed after a sufficient amount of solvent had distilled off to change the Hansen solubility parameter and allow the ink to gel, if a solvent was present in the formulation to adjust the Hansen solubility parameter. For gels or in the case of formulations without solvent, this is done for gels after a sufficient time.
The hardness is read 15 minutes after the weight of the sample has become constant, which means that the sample has lost all of the solvent and has reached the highest hardness of the gelled ink.

  This possibility of reading the hardness of the gel has been found to be a very important physical difference between the inks of the present invention and known inks based on viscosity increase when the solvent is distilled off. . In fact, all attempts to read very high viscosity offset inks are not stable, even when hardness values are detected on the first reading, and the durometer sinks into the viscous ink. First, it failed for all types of colors to drop to the point where it could no longer be read each time it was repeated. This is because viscous inks do not establish a gelled base for reading.

  The gel hardness measurements in FIG. 12 very well explain the results obtained, with only the yellow ink having sufficient consistency to support the overprinting process. In fact, it has been found that the hardness of the gel also depends on the type of pigment used. The same composition may provide a gel with sufficient hardness when a yellow pigment is used, and may provide a gel that is not sufficiently hard as discussed below when a black pigment is used. .

  When the composition of Formula A was modified to include a higher amount of polymer, the trapping value was dramatically improved as shown in Example 2 below.

  Gel hardness versus gelling agent concentration for polyvinyl butyral (Butvar B76) is somewhat linear for a selected percentage interval, but when the hardness drops to less than 5-6 at Shore 00 It is impossible to read the gel structure and consistency because they tend to sink into the ink without being able to support the measuring device. Below this lower limit, i.e. below 4 at Shore 00, it was found by conducting empirical tests that the gel strength can no longer support the flexo overprinting process.

  The unusual behavior of black ink can be explained as follows. Typical carbon black pigments have Hansen solubility parameters such that they readily adsorb common solvents and / or polymers. This can easily affect the Hansen solubility parameter of the liquid phase in the ink. Absorption of the polymer results in a rapid viscosity increase, in particular because, for example, the molecular weight of carbon black with two adsorbed polymer molecules is approximately twice that of individual polymer molecules. The effect of doubling molecular weight on viscosity is greater than that of two individual polymer molecules.

Data for most conventional carbon blacks show the following Hansen solubility parameters: δP: 6 (Mpa ³ ) ^1/2 and δH 5.5 (Mpa ³ ) ^1/2 for carbon black, and the overall Hansen solubility parameter Is within the dissolving capacity of polyvinyl butyral (Butvar B76).

  Since the use of black was programmed to be the last printed color in all printing tests, the results were not affected by insufficient gel hardness. In order to overcome the trapping problem of the first formulation and incorporate the information obtained from the hardness evaluation, a new formulation was prepared using 2.5% polyvinyl butyral in all colors as follows.

(Example 2): Ink using increased amount of polymer In Example 2, the amount of polymer was increased. That means increasing the amount of change in polymer network density and Hansen solubility parameters to ensure sufficient spacing between the liquid and gel state to avoid gelling of ink in the inking system. Table 7 shows Formulation B.

Manufactured in Comexi FW 1508 at a production rate of 350 m / min using only cold air in an interstation dryer and in the EZCure-I DF ^{trademark from} ESI (Energy Sciences Inc.-Wilmington, Mass.) And cured at 20 kGy.

The printed material was tested for adhesion. The results are shown in Table 8 below.

  The main change from the previous formulation to this (Formulation B) is that the amount of polymer (polyvinyl butyral-Butvar® B76) is from 0.5% to 2.0% and the amount of solvent is from 5%. That is up to 10%.

  When considering a new formulation, in formulation A the amount of non-reactive solvent would move the Hansen solubility parameter of the final liquid mixture to a point well inside the PVB dissolution region to ensure correct solubilization. It was clear that it was not enough. This was not so obvious in the initial formulation due to the amount of PVB in the formulation.

The level of solvent required to accommodate the lowest level of solubilization was 17% of the liquid compound (10% of total Formulation B) instead of 8.2% of the liquid formulation or 5% of the total formulation. %). Table 9 below shows the new situation for Hansen solubility parameters for Formulations B1 (before solvent evaporation) and B2 (after solvent evaporation).

The trapping results here are greatly improved as can be seen from the following values.

  As the data above shows, the trapping value is far above the minimum desired trapping, and is excellent despite the many stop and run operations during the printing run. Showed stability. This operation is the worst scenario for testing trapping stability.

The Hansen solubility parameter in Formulation B1 shows a good dissolution effect on the polymer (PVB) ensuring correct solubilization without a noticeable tendency for gel formation. After evaporation, the trapping value was considered very satisfactory and stable, even by only using cold air in Comexi FW 1508 up to 350 m / min. The change in Hansen solubility parameter is shown below.

Example 3: Compositions approved for food packaging Using the same general formulation principle except that only FDA approved monomers for food packaging are used, HDDA is treated with TRPGDA (tripropylene glycol dipropylene). The previous formulation was changed by exchanging with (acrylate).

The use of HDDA and / or TRPGDA, in both cases, to reduce the level of methoxypropanol (Dowanol PM) in the ink as much as possible, as it has an adverse effect on volatile organic compounds in the atmosphere after its evaporation. Is brought as close as possible to the solubility boundary of Butvar® B76. Table 10 shows Formulation C.

Manufactured in Comexi FW 1508 at a production rate of 350 m / min using only cold air in an interstation dryer and in the EZCure-I DF ^{trademark from} ESI (Energy Sciences Inc.-Wilmington, Mass.) And cured at 20 kGy.

The printed material was tested for adhesion. The results are shown in Table 11 below.

Toward the evaluation of Hansen solubility parameters, Table 12 below shows these changes before and after solvent evaporation.

The change in Hansen solubility parameter is shown below.

The trapping tone obtained was also good enough for the flexographic printing process as shown in the following results.

  Based on the concepts described in the present invention, many formulation changes of the type described herein can be implemented by those skilled in the art. There are a number of choices regarding non-reactive solvents, solvent soluble resins, monomers and oligomers that permit compliance with the claims of the present invention. Also, Hansen solubility parameters for many other monomers and oligomers are currently unknown. Such data will assist in developing ink formulations within the scope of the present invention without requiring much testing.

Claims (6)

Flexographic printing process including the following steps:
a) printing on a substrate a first layer of radiation curable ink suitable for wet-on-wet flexographic printing; said ink being non-reactive other than one or more non-reactive polymers and one or more water the solvent includes in combination with one or more reactive monomers and / or oligomers, pigments, and additives, whereby the polymer over, the monomer over and / or oligomers over and non-reactive solvent other than the water It is dissolved in,
b) Ink in the first ink layer in that the printing was a gel state, the ink layer of the first comprising the steps of gel ink layer, the gel ink layer, supports the ink layer definitive future print step Having sufficient hardness; the change to the gel state is due to changing Hansen solubility parameters by at least partial evaporation of the solvent in the ink, the sufficient hardness being a rubber of ASTM D2240-05 At least OO 4/1 according to standard test methods for properties,
c) Subsequently, a second ink layer in a liquid state is printed on at least a part of the pre-gelled first ink layer, and the second ink layer is printed on at least part of the solvent in the ink. Changing to a gel layer by changing Hansen solubility parameters by selective evaporation ,
d) step of the step a) to c all of a series of ink layer following the), all the colors are printed in the same step as the step a) to c) until the time it is applied onto the substrate,
e) Step of simultaneously curing all ink layers using EB or UV radiation at the end of step d) . Flexographic printing process including the following steps:
a) printing on a substrate a first layer of radiation curable ink suitable for wet-on-wet flexographic printing; said ink comprising one or more non-reactive polymers and one or more reactive monomers and / or Including in combination with oligomers, pigments, and additives, whereby the polymer is only partially soluble in the monomers and / or oligomers;
b) Ink in the first ink layer in that the printing was a gel state, the ink layer of the first comprising the steps of: a gel ink layer, the gel ink layer, supports the ink layer definitive future print step sufficient The change to the gel state is due to (i) a reduction in shear force applied to the ink and / or (ii) a temperature drop in the ink, the sufficient hardness being a rubber of ASTM D2240-05 At least OO 4/1 according to standard test methods for properties,
c) Subsequently, a second ink layer in a liquid state is printed on at least a part of the first gel layer that has been previously gelled, and (i) a shearing force is applied to the ink. And / or (ii) changing the gel layer by a temperature drop in the ink ;
d) step of all the series of ink layer following the step a) to c), all the colors are printed in the same step as the step a) to c) until the time it is applied on the substrate,
e) Step of curing all ink layers simultaneously using EB or UV radiation at the end of step d) . When the ink is usually a gel, the first gel is reversibly broken by shear forces in the application process to provide a liquid ink for flexographic printing, which is applied to a substrate to be printed 3. The flexographic printing process of claim 2 , wherein the flexographic printing process of claim 2 wherein the gelled ink returns to the gel state simultaneously and the gelled ink has a hardness of at least 4 degrees on Shore OO according to ASTM D2240-05 standard test method for rubber properties. Adjusting the Hansen solubility parameter of the ink to first provide a liquid ink containing pigment for flexographic printing, and then altering the printed ink layer in the printed ink to a gel, The flexographic printing process according to claim 1. The final curing step at the end of the process is based on irradiation that cures all ink layers, said irradiation being generated by an ultraviolet source and an electron beam device having radiation in the wavelength range comprised between 200 nm and 400 nm It is selected from electrons, flexographic printing process according to any one of claims 1 to 4. The flexographic printing process according to any one of claims 1 to 5 , wherein the gel hardness is at least 7 on Shore OO .